The Flash — “Running to Stand Still” — Image: FLA209A_0027b.jpg — Pictured (L-R): Wentworth Miller as Leonard Snart, Mark Hamill as James Jesse/Trickster and Liam McIntyre as Mark Mardon– Photo: Cate Cameron/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209A_0017b.jpg — Pictured: Mark Hamill as James Jesse/Trickster — Photo: Cate Cameron/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209A_0038b.jpg — Pictured: Wentworth Miller as Leonard Snart — Photo: Cate Cameron/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209A_0138b.jpg — Pictured: Liam McIntyre as Mark Mardon — Photo: Cate Cameron/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209A_0144b.jpg — Pictured: Liam McIntyre as Mark Mardon — Photo: Cate Cameron/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209A_0261b.jpg — Pictured: Shantel VanSanten as Patty Spivot — Photo: Cate Cameron/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209A_0273b.jpg — Pictured: Grant Gustin as The Flash — Photo: Cate Cameron/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209A_0288b.jpg — Pictured (L-R): Shantel VanSanten as Patty Spivot and Grant Gustin as The Flash — Photo: Cate Cameron/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209b_0264b.jpg — Pictured (L-R): Grant Gustin as Barry Allen and Candice Patton as Iris West — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209b_0206b.jpg — Pictured (L-R): Danielle Panabaker as Caitlin Snow and Teddy Sears as Jay Garrick — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209b_0173b.jpg — Pictured: Jesse L. Martin as Detective Joe West — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image FLA209b_0146b.jpg — Pictured (L-R): Shantel VanSanten as Patty Spivot and Grant Gustin as Barry Allen — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209b_0131b.jpg — Pictured (L-R): Teddy Sears as Jay Garrick and Danielle Panabaker as Caitlin Snow — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image FLA209b_0100b.jpg — Pictured: Candice Patton as Iris West — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209b_0097b.jpg — Pictured (L-R): Candice Patton as Iris West, Jesse L. Martin as Detective Joe West and Keiynan Lonsdale as Wally West — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209b_0071b.jpg — Pictured: Grant Gustin as Barry Allen — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209b_0021b.jpg — Pictured: Wentworth Miller as Leonard Snart — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image FLA209b_0014b.jpg — Pictured (L-R): Wentworth Miller as Leonard Snart and Grant Gustin as Barry Allen — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

The Flash — “Running to Stand Still” — Image: FLA209b_0218b.jpg — Pictured (L-R): Candice Patton as Iris West and Grant Gustin as Barry Allen — Photo: Katie Yu/The CW — © 2015 The CW Network, LLC. All rights reserved.

Official Synopsis:

“Running To Stand Still” — (8:00-9:00 p.m. ET) (HDTV)

MARK HAMILL, WENTWORTH MILLER AND LIAM MCINTYRE RETURN; KEIYNAN LONSDALE JOINS THE CAST AS WALLY WEST — When Mark Mardon AKA The Weather Wizard (guest star Liam McIntyre) returns to break Leonard Snart AKA Captain Cold (guest star Wentworth Miller) and James Jesse AKA The Trickster (guest star Mark Hamill) out of Iron Heights, Barry (Grant Gustin) must stop these rogues from taking over Central City during Christmas. Meanwhile, Joe (Jesse L. Martin) and Iris (Candice Patton) meet Wally West (Keiynan Lonsdale). Kevin Tancharoen directed the episode written by Andrew Kreisberg (#209). Original airdate 12/8/2015.